Cams

ABSTRACT

A cam defining a longitudinally-extending cam track, and including a central portion underlying and defining the center of the cam track, and side portions on opposite sides of the central portion underlying and defining respective side portions of the track, each of the side portions being a layer of relatively high yield point material and of substantial thickness overlying a core of relatively low yield point material, and the central portion being either the core or a thin layer of relatively high yield point material overlying the core.

United States Patent [191 Denker Nov. 19, 1974 [54] CAMS OTHERPUBLICATIONS Inventor: James Denke"! Scimate, Mass- Rothbart, H. A.Cams. N.Y., John Wiley & Sons, Inc., [73] Assignee: Nutron Corporation,Hingham, 1956- 275-282- T1206 R6 Mass. Primary Examiner-Samuel Scott[22] Flled: 1973 Assistant ExaminerF. D. Shoemaker Appl. No.: 327,651

[52] U.S. Cl. 74/567, 308/241 [51] Int. Cl. Fl6h 53/00 [58] Field ofSearch 74/567; 91/501; 308/241 [56] References Cited UNITED STATESPATENTS 340,156 4/1886 Richards 74/567 X 475,379 5/1892 1,353,368 9/1920Williams 74/567 X 2,729,117 H1956 Maybach et a1. 3,058,369 10/1962 Vogel74/567 X s7 1 ABSTRACT A cam defining a longitudinally-extending camtrack, and including a central portion underlying and defining thecenter of the cam track, and side portions on opposite sides of thecentral portion underlying and defining respective side portions of thetrack, each of the side portions being a layer of relatively high yieldpoint material and of substantial thickness overlying a core ofrelatively low yield point material, and the central portion beingeither the core or a thin layer of relatively high yield point materialoverlying the core.

11 Claims, 7 Drawin Finn-g pmgm xsv 1 91974 3848,48

semen; 2

FIG. 2A

FIG. 3A "FIG. 3

4A FIG. 4B

CAMS

This invention relates to cams.

It is a primary object of the present invention to provide aninexpensive undulating cam track having a greatly increased loadcarrying capacity. Other objects include providing multi-cycle cams,especially useful in rotary fluid pumps and motors, which are finallycontoured during motor operation without destruction of their necessaryconfiguration.

The invention features a longitudinally-extending cam track, andincluding a central portion underlying and defining the center of thecam track, and side portions on opposite sides of the central portionunderlying and defining respective side portions of the track, each ofthe side portions being a layer of relatively high yield point materialand of substantial thickness overlying a core of relatively low yieldpoint material, and the central portion being either the core of a thinlayer of relatively high yield point material overlying the core. Inpreferred embodiments, the thickness of the layer of relatively highyield point material defining the sides is not less than on the order ofan order of magnitude greater than that of any high yield point materialat the track center.

Other objects, features, and advantages will appear from the followingdetailed description of preferred embodiments of the invention, taken inconjunction with the attached drawing, in which:

FIG. 1 is a longitudinal cross-sectional view of a rotary fluid motorincluding a cam constructed in accordance with the present invention;

FIGS. 2A and 2B are cross-sectionalviews of the cam of the motor of FIG.1 at two stages of the manufacture thereof; and,

FIGS. 3A, 3B, and 4A and 4B are cross-sectional views of, respectively,two other cams embodying the present invention, each at two stages ofthe manufacture thereof.

Referring more particularly to the drawings, there is illustrated arotary fluid motor, generally designated 10, comprising an output shaft12 extending coaxially through a multi-part housing including, incoaxial alignment, a cylindrical main housing 14, a cylindrical supporthousing section 16, and an end plate 18. The construction of motor isillustrated in detail, in my US. Pat. No. 3,662,551, issued on May 16,1972, which is hereby incorporated by reference, and will be de scribedbut briefly herein.

A stepped cylindrical fluid distribution manifold and rotor 22 aremounted within annular cavities within main housing 14 and surroundingshaft 12. One axial face 24 of rotor 22 is in face-to-face engagementwith the adjacent face 26 of manifold 20. Rotor 22 is fixed on shaft 12for rotation therewith by spline 28.

Main housing 14 includes drilled inlet and outlet drain conduits,designated 30 and 32 respectively, extending through the wall of themain housing section. The outer portion of each conduit is tapped forreceiving a fluid coupling. A pair of axially spaced, radially axiallywithin manifold 20 from surface 26 to channel 7 38. A total of sixadditional drilled conduits 44, extending axially within manifold 20from surface 26 to channel 40, are provided in the ring, spaced midwaybetweenadjacent ones of conduits 42.

v Rotor 22 includes a total of ten cylindrical bores 50 and 10cylindrical conduits 52 (arranged in a ring within the'rings of bores50) extending axially through the full thickness of the rotor. A drilledconduit 54 extends from each conduit 52 'to the bore 50 alignedtherewith. Two steel balls 56 are fitted within each of bores 50 formovement within the bore.

An annular wave cam 60, 62 including circular undulating ball-engagingsurface 61, 63 is mounted on each axial side of rotor 22, coaxiallytherewith, with the ballengaging surfaces or tracks 61, 63 of each camengaging one of the balls 56 in each bore 50. Each track 61, 63 is atrapezoidal acceleration cam surface comprising alternating parabolicand intermediate fairing sections. The period of the cam is 60 (that is,each entire annular track includes 6 substantially identical completecycles each having one high point or peak and one low point or valley)and its total amplitude (peak-to-valley) is slightly less than one-halfthe diameter of balls 56.

In operation, fluid is introduced into the motor at high pressurethrough conduit 30, and exits from the motor at low pressure throughconduit 32. A power stroke of the balls 56 within a bore 50 commenceswhen the balls engage a crest or high point of the cam tracks 61, 63 ofwave cams 60, 62 and, therefore, are in their nearest relative position.With the balls in this position, high pressure fluid from inlet conduit30 passes from the inlet through annular channel 38, conduits 42 ofmanifold 30, and rotor conduits 52, 54 into inwardly facing annularchannels 38, 40 are provided in housing section 14 at the periphery ofmanifold 20.

A total of six drilled conduits 42, arranged in a ring and spaced atregular 60 intervals therearound extend the bores 50, thereby forcingthe balls within the bore away from each other against the tracks 61, 63of wave cams 60, 62. The force of the balls against the ballengagingsurfaces imparts a torque to, and causes rotation of, the rotor 22. Asthe rotor rotates, balls 56 roll down the slopes of the ball-engagingsurfaces with which they are in contact, the balls within each bore 50thereby moving apart. When, after 30 rotation of rotor 24, the ballshave reached their most distant relative position, the port of conduit52 moves out of communication with conduit 42 and into communicationwith adjacent conduit 44 in manifold 20. Conduit 44 is connected,through channel 40, to low pressure fluid outlet conduit 32. During thenext 30 rotation of rotor 22, balls 56 roll up the slope of the tracks61, 63 thereby moving together and discharging fluid from the bore 50into the outlet.

The power produced by motor It] depends in large measure on the forcewith which the fluid in bores 50 drives the balls 56 outwardly againstcams 60, 62. Greater force results in a larger power output, but themaximum force that can be applied is limited by the load-carryingcapacity of the piston-track contact area.

In devices using ball pistons, one method of increasing theload-carrying capacity has been to contour the track to the ball piston,so that the area of contact, under load, between the ball and track willbe elliptical, the major axis of ellipse being transverse to thedirection. of relative movement of the ball along the cam track. Thismethod is especially useful with simple carns of soft (low yield point)material. The material will undergo plastic deformation at relativelylow stress, and the force of the balls against the track willplastically deform any areas of localized high stress, and conform thetrack to the ball. Such deformation is very useful in smoothing outminor manufacturing flaws. However, it will also flatten the peaks (highpoints) of undulating or multi-cycle cam tracks, thereby destroyingtheir basic necessary configuration.

A second method of increasing load-carrying capacity, which has beenuseful with multi-cycle cams, is to raise the yield point of thematerial defining and underlying the cam track by case-hardening,thereby providing a hard (high yield point) case-hardened layer ofsubstantially uniformv thickness underlying the cam track surface. Ascase-hardened material will not yield plastically, the problems ofdeformation inherent in soft multicycle cams are eliminated. However,lack of plastic deformation also requires that the track, asmanufactured, be perfectly contoured to the ball with which it will beused, a difficult and expensive procedure..If contour is not perfect,the ball-track contact area will be relatively small and the force ofthe piston against the track will create localized destructive stressesin excess of the case-hardened material's yield point.

Cams constructed according to the present invention combine theadvantages, and eliminate the drawbacks, of both these methods byproviding a case-hardened layer of conventional thickness underlying thesides of the finished cam track, but only a very thin casehardenedlayer,'or no case-hardened layer at all, underlying the central portionof the track which defines most or all of the surface actually contactedby the ball pistons. Such cams are manufactured by casehardening anunfinished cam to form a case-hardened layer or shell of substantiallyuniform thickness overlying an unhardened core at the surface that willeventually define the finished cam track, and then removing a portion ofthe case-hardened layer to form the finished track. The exact shape ofthe original cam will depend on the desired configuration of thefinished track, which in turn depends on the radius of the ball to beused therewith. The unfinished cam is initially formed with the surfacethereof which will eventually define the finishedlongitudinally-extending track having a greater curvature, in transversecross-section, than that of the finished track. The curvature of asurface, of course, is equal to l/R, where R is the radius of curvatureof the surface, and R is positive or negative depending on whether thevector from the surface to the center of curvature extends into or awayfrom the solid body defining the surface. Thus, a convex surface haspositive curvature; a concave surface, negative. The curvature of flatsurface is zero, its radius of curvature being infinite.

As shown in FIG. 2A, cam 60 is initially rough formed with the annularsurface 70 thereof which eventually will define cam track 61 defining aroughcam track having the same number of cycles or undulations as willtrack 61.

In transverse cross-section, the curvature of surface 70 is about-3.2/in. (concave with R of about 5/16 inch); that of finished track 61(FIG. 2B) is slightly less than 4.0/in. (for use with balls of 0.500 in.diameter). After rough forming, cam 60 is case-hardened, in anyconventional manner, to form a case-hardened layer 72, on the order of0.010 inch to 0.020 inch thick, surrounding a central unhardened core74.

To form the finished cam track 6l,'a major portion of the case-hardenedlayer is removed, using conventional machining techniques and cutters oflesser radius of curvature than surface 70. Typically, the majormachining is done with a ball mill of slightly smaller radius thanfinished track 61, and final finishing is accomplished with a bandgrinder. After finishing, the thickness of the case-hardened layerunderlying track surface 61 varies from a minimum of 0.001 inch to 0.002inch, at the center of the track, to almost the original thickness oflayer 72, 0.010 inch to 0.020 inch, under the track sides. The radius ofcurvature of the finished track is slightly greater than that of balls52.

In operation, balls 56 are forced against and roll along cam surface 61,generally centered thereon. The

pressure of the balls plastieally deforms the unhardened core materialunder the thin case-hardened material along the center of the track,thereby providing the desired elliptical contact area. The thincase-hardenedv layer elastically deforms, acting as a sort of cover forthe underlying plastically deformed soft material. The thickcase-hardened layers along the sides of the track elastically deform,but resist destructive plastic deformation of the basic multi-cycle camconfiguration.

Reference is now made to FIGS. 3A,-and 3B, and 4A and 4B, whichillustrate slightly modified process for manufacturing cams of thepresent invention.

As shown in radial cross-section in FIG. 3A, cam 60' is initiallyrough-formed with the annular surface thereof which will eventually formthe finished cam track surface 61 (FIG. 48) having, in radial transversecross-section, a slight positive (convex) curvature. The rough cam 60"shown in FIG. 4A is initially formed with a radially projecting flangeprojecting upwardly from the center of annular surface 70". Each roughcam is then case-hardened to form a case-hardened layer, 72', 72"respectively, surrounding a respective unhardened core 74, 74".

To finish cam 60', a portion of the case-hardened layer 72 underlyingsurface 70 is removed, using conventional machining techniques. A ballmill and band grinder maybe employed as previously discussed withreference to cam 60 to form the concave finished cam surface 61(negative curvature) shown in FIG. 38. If desired, a flat finished camtrack (zero curvature) may also be formed. In either case, enough ofcasehardened layer 72' is removed so that the thickness of the remainingcase-hardened material will be very thin (or perhaps zero) at the centerof the finished cam surface, and will be almost as thick as the originallayer along the track edges.

To finish cam 60", flange 80 is removed, using a conventional milland/or grinder to form the flat finished track 61", shown in FIG. 4B,which is defined at its longitudinally-extending side portions onopposite sides of said central portion underlying and definingrespective side portions of said track,

each of said side portions being a layer of relatively high yield pointmaterial and of substantial thickness overlying a core of relatively lowyield point material, and

said central portion being one of said core and a thin layer of saidrelatively high yield point material overlying said core.

2. The cam of claim 1 wherein each of said layers of relatively highyield point material is a case-hardened layer and said core ofrelatively low yield point material is an unhardened core.

3. The cam of claim 2 including a continuous casehardened layer ofvarying thickness extending transversely the width of said track.

4. The cam of claim 3 wherein the thickness of said layer is on theorder of 0.00] inch to 0.002 inch at the center of said track and on theorder of 0.010 inch to 0.020 inch at the sides of said track.

5. The cam of claim 2 wherein the center of said track is defined bysaid unhardened core.

6. The cam of claim 2 wherein the thickness of said layers underlyingsaid side portions is on the order of 0.010 inch to 0.020 inch and thethickness of said thin layer is less than 0.005 inch.

7. The cam of claim 2 wherein the thickness of said layers underlyingsaid side portions is on the order of 0.010 inch and 0.020 inch and saidcentral portion is defined by said core.

8. The ca'm of claim 2 wherein said track is undulat- 9. The cam ofclaim 2 wherein said track is annular.

10. The cam of claim 1 wherein said track is nonconvex in transversecross-section.

11. The cam of claim 10 wherein said track is concave in transversecross-section.

1. A cam defining a longitudinally-extending cam track, said camincluding a central longitudinally-extending portion underlying anddefining the center of said track and longitudinally-extending sideportions on opposite sides of said central portion underlying anddefining respective side portions of said track, each of said sideportions being a layer of relatively high yield point material and ofsubstantial thickness overlying a core of relatively low yield pointmaterial, and said central portion being one of said core and a thinlayer of said relatively high yield point material overlying said core.2. The cam of claim 1 wherein each of said layers of relatively highyield point material is a case-hardened layer and said core ofrelatively low yield point material is an unhardened core.
 3. The cam ofclaim 2 including a continuous case-hardened layer of varying thicknessextending transversely the width of said track.
 4. The cam of claim 3wherein the thickness of said layer is on the order of 0.001 inch to0.002 inch at the center of said track and on the order of 0.010 inch to0.020 inch at the sides of said track.
 5. The cam of claim 2 wherein thecenter of said track is defined by said unhardened core.
 6. The cam ofclaim 2 wherein the thickness of said layers underlying said sideportions is on the order of 0.010 inch to 0.020 inch and the thicknessof said thin layer is less than 0.005 inch.
 7. The cam of claim 2wherein the thickness of said layers underlying said side portions is onthe order of 0.010 inch and 0.020 inch and said central portion isdefined by said core.
 8. The cam of claim 2 wherein said track isundulating.
 9. The cam of claim 2 wherein said track is annular.
 10. Thecam of claim 1 wherein said track is non-convex in transversecross-section.
 11. The cam of claim 10 wherein said track is concave intransverse cross-section.